Stepper Motor ID - Novatronics 20M34R1-A

Discussion in 'General Electronics Chat' started by tracecom, Aug 4, 2011.

  1. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
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    I bought this stepper motor from All Electronics. They don't have much info on it and Google doesn't turn up anything that's not on the All Electronics site.

    It's a five wire motor with resistances as shown in the attached table. I have confirmed that the black wire is common and the stepping order is red, orange, yellow, brown.

    The motor is very different from the (few) other steppers I have experimented with. (1) It doesn't seem to have permanent magnets; when the shaft is manually rotated, there is no perceptible feeling of steps or resistance of any sort. (2) The step angle seems to be 15°. (3) The torque seems to be very low for a motor of this size, but since I don't know the proper operating voltage, I am using only 5vdc.

    Any insight (or firsthand knowledge) about this motor would be appreciated.
     
    Last edited: Aug 4, 2011
  2. #12

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  3. tracecom

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    I called them twice and, in my nicest voice, told them what I wanted, and left my phone number and e-mail address on the answering machine, but received no response. My guess is that everyone who buys one of these, and maybe many who don't, call and ask for info, and maybe Novatonics just doesn't bother to reply.
     
  4. #12

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    Sometimes buying "on the cheap" gets you stuck with stuff you can't use. Sorry about that. I can only hope that Novatronics eventually responds to your phone calls.
     
  5. tracecom

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    Well, I actually bought it long after trying to contact them. My curiosity just got the better of me and I bought it on a whim; it's not the only useless piece of junk I own. :D
     
  6. #12

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    Glad you have a good attitude about this. Everybody has a junk box.
     
  7. tracecom

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    With all the intellect on this forum, someone will come up with great information. I wouldn't be surprised if the designer of the motor was a member here.
     
  8. shortbus

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    When you said the motor has no magnets or 'detents' when turned by hand is the give away :) It's probably a "variable reluctance" stepper. While most have 4 leads they do make 5 and 6 lead motors, that way. Heres one link of many; http://zone.ni.com/devzone/cda/ph/p/id/287#toc2
     
  9. tracecom

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    Thanks. I think you are correct.

    Further testing shows that there is no holding torque when power is removed from the motor. I have briefly tried the motor at 5 vdc and 12 vdc with no ill effects. The holding torque at 12 vdc is substantial (as determined by my non-calibrated thumb and index finger.) However, at 12 vdc, it draws 560 ma, which is above the capability of a ULN2803.

    The motor must weigh close to a pound. I think it may be a multi-stack configuration.
     
  10. THE_RB

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    It's a variable reluctance motor, and looks to be quite a nice quality one. :)

    Shame it doesn't have mounting flange holes but you can still mount it in some type of circular clamping plate etc.

    That motor size will be rated around 7 watts per phase for "2 phase on" full step operation. Your 12v 560mA sounds almost perfect.
     
  11. tracecom

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    Thanks for the information. I'll have to locate some darlington pair IC that will handle that much current.
     
  12. shortbus

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    Why not use mosfets? In the low side switch that you need it is a simple configuration.
     
  13. tracecom

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    That's a good idea, but the only ones I have on hand are IRLZ44N. That's kind of overkill, but since I do have them...

    I want to control the motor from a PICAXE, so I guess a 330 ohm resistor to the gate of the MOSFET with a 100k pulldown resistor, times four (one for each of the motor phase windings).
     
  14. #12

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    Hey, I once used an IRF510 on a motorcycle relay because that's what I had laying around. Overkill is not a problem. You can always unsolder your good parts if you ever buy lesser mosfets.
     
  15. THE_RB

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    You can use a ULN2804 which (based on my memory!) is the same as the 2803 but it has 8 darlingtons inside so you can parallel them in pairs to get more current.

    Of you might want to look at the LiniStepper- it's an open source *microstepping* stepper motor driver I designed back in 2000 or so, and being open source you can adapt it to the PICAXE.

    http://www.piclist.org/techref/io/stepper/linistep/index.htm

    Actually check the PICAXE forum I think someone may have done a PICAXE Linistepper conversion before, but again based on memory. ;)
     
  16. tracecom

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    Actually, the ULN2803 has 8 channels so I can use one of those with the channels doubled as you suggest. Thanks again.
     
  17. MrChips

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    From what you describe this sounds like a straight forward four-phase unipolar 12V stepping motor.

    BLACK - COMMON - connect to +12V
    BROWN - PHASE1 - connect to collector or drain of Phase 1 driver
    RED - PHASE 2 - etc
    ORANGE - PHASE 3 - etc
    YELLOW - PHASE 4 -etc

    Each driver is a common-emmiter BJT sink to ground or a HEXFET sink to ground.
    Drive each driver from a logic signal via a 1K resistor to the base or gate.

    I like to use a microcontroller to drive a stepping motor so that I can control the speed and travel.

    You only need two bits output. If OutputA drives PHASE1 and OutputB drives PHASE2
    the step sequence is

    A B
    0 0
    1 0
    1 1
    0 1
    0 0
    etc

    Phase 3 is driven by NOT A
    Phase 4 is driven by NOT B

    At any instant, two coils are always energized.
    Reverse the phase pattern to step in the reverse direction.
    To get up to maximum speed you have to start slow and then increase the stepping rate.

    Hope this works for you.
     
  18. tracecom

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    I feel certain this will work. In fact the PICAXE has a "toggle" command just for purposes like this. Thanks.

    Code ( (Unknown Language)):
    1. 'Drive unipolar stepper motor in single steps
    2. 'but with increased torque. PICAXE-08M
    3.  
    4. symbol delay = 1        'pause duration (must be at least 1 ms.)
    5. let dirs = %10110    'sets pins 4, 2, and 1 as outputs
    6.                 'pin 3 is always an input; pin 0 is always an output
    7.  
    8. cw:                'clockwise rotation
    9.     toggle 0
    10.     pause delay
    11.     toggle 1
    12.     pause delay
    13.     goto cw        'endless loop
     
  19. SgtWookie

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    Jul 17, 2007
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    The ULN2003/ULN2803 isn't up to the task; it'll die on you.
    The ULN2064 thru ULN2076 are quad Darlington drivers capable of sinking 1.5A per channel. A ULN2064 would work OK; much better than a ULN2803/ULN2003, but not as good as logic level power MOSFETs.

    The Darlington drivers will have a Vce of over a volt at 500mA+ Ic; and that translates to wasted power.

    If you want to consider the MOSFET route, have a look at these little gems:
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=IRLU8721PBF-ND
    30V, 65A, logic level gate in a nice, compact TO-251AB long-lead package; it looks sort of like a small TO-220 package without a big tab. I'm pointing these out because they have a very low gate charge which makes them very easy to drive from a microcontroller, and the Rds(on) is so low (11.8m or less at Vgs=4.5v) that you'll have minimal power dissipation as heat (practically none with 600mA current), and you'll only lose about 6mV instead of over a volt like with the Darlingtons.

    If you buy 10, they're under $0.75/ea
     
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